Lab Activity 7

Bone HistologyMartini Chapter 6Lab Activity 71Divisions of skeletal systemAxial skeleton: in the vertical axis of the body. Consists of the skull, hyoid bone, vertebral column ribs and sternum.Appendicular skeleton: skeleton attached to the axial skeleton

Bone featuresOnes have many surface features that have specific names.Grouped by projections, depressions, or holes in the bone.Some projections:Some articulate with other bonesAre attachment sites

MarkingDescriptionExampleHeadBony expansion carried on a narrow neckFemur CondyleRounded articular projectionCondyle of mandibleFacetSmooth, nearly flat articular surfaceFacet of ribsRamusArmlike bar of boneRamus of mandibleProjections for Muscle & Ligament AttachmentProcessAny bony prominenceTrochanterVery large, blunt, irregularly shaped processFemur TuberosityLarge, rounded projection; may be roughenedTibia , ischiaTubercleSmall, rounded projection or processAdductor tubercle of femur (distal end)CrestNarrow ridge of bone; usually prominentAnterior crest of tibiaLineNarrow ridge of bone, less prominent than a crestIntertrochanteric lineSpineSharp, slender, often pointed projectionSpinous process of vertebraEpicondyleRaised area on or above a condyleMedial epicondyle of femur

Bone4Organic and inorganic materialThe organic portion is composed mostly of cells and collagenous fibers (1/3 volume by weight)The inorganic portion consists mainly of hydroxyapatite.Calcium salts, which contribute hardness and rigidity.Make bones as strong as steel or reinforced concrete.intercellular matrix of bone tissue is arranged in multiple layers called lamellae

Classification of Bones by Shape5Long bones: longer than they are wide (e.g., humerus, metacarpals )Consists of a shaft (diaphysis) plus 2 expanded ends (epiphysis).

5Features of Long bones 6Hyaline cartilageCovers joint surface of epiphysisCushions opposing bone endsAbsorb stress

6Features of Long Bones7Diaphysis: shaft forms the long axis of the boneWall of compact bone surrounding a medullary (marrow) cavity Epiphyses: expanded bone endsArticulates with another boneExterior made of a thin layer of compact boneInterior made of spongy bone78

8Bone Marrow9MarrowNetlike mass of connective tissue that fills the spaces of bone Medullary cavities of long bonesIrregular spaces of spongy bone9Bone Tissues Red Marrow10Hemopoietic tissueFormation of red blood cells, white blood cells, and blood plateletsIn infantsFound in the medullary cavity and all areas of spongy bone In adultsFound in the diplo of flat bones, and the head of the femur and humerus10Bone Tissues Yellow Marrow11As we age, the bone marrow is replaced by fat storesRed becomes yellow marrowInactive in blood cell productionFunctions in shock absorption11Structure of Short, Irregular, and Flat Bones12Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the insideHave no diaphysis or epiphysesContain bone marrow between the trabeculae

12Bone Membranes13Periosteum: Double-layered protective membraneOuter fibrous layer is dense irregular connective tissueInner osteogenic layer is composed of osteoblasts and osteoclastsRichly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foraminaSecured to underlying bone by Sharpeys fibers (strands of collagen)

13Bone Membranes14Endosteum: Delicate membrane covering internal surfaces of boneCovers the trabeculae of spongy bone in the marrow cavities and lines the canals that pass through compact bone.Lines the medullary cavityContains both osteoblasts and osteoclasts.

14Classification of Bones by Shape15Short bonesCube-shaped bones of the wrist and ankle

Sesamoid bonesBones that form within tendons (e.g., patella)

15Classification of Bones by Shape16Flat bones: Thin, flattened, and a bit curved (e.g., sternum, and most skull bones)

Sternum16Classification of Bones by Shape17Irregular bones: bones with complicated shapes (e.g., vertebrae and hip bones)

Sphenoid Bone17Classification of Bones by Shape18Wormian or sutural bones: Tiny bones between cranial bones.Vary in number and location in different people

18Bone Tissue: Compact Bone19Bones are composed of both compact and spongy bone tissueCompact bone is found where great strength is needed.It makes up the external surfaces of all bones and the shafts of long bones.

19Bone Tissues: Spongy Bone20Honeycomb of small needle-like pieces called trabeculae.Organized in an open frameworkProvides considerable strength with reduced weightThe open spaces between the trabeculae are filled with bone marrow

2021

Note the gross differences between the spongy bone and the compact bone in the above photo.Do you see the trabeculae?2122

Compare compact and spongy bone as viewed with the light microscope

22Microscopic Structure of Compact Bone 23Bone tissue is composed of repeating, circular units called Haversian systems or osteons Osteons are the structural unit of compact boneThe substance of compact bone is formed from many osteons cemented together Oriented parallel to the long axis of the bone, and parallel to the forces upon that bone

23Microscopic Structure of Compact Bone24

24Haversian System (Osteon) Components25Concentric Lamella: Weight-bearing, column-like matrix tubes composed mainly of collagen that surround the central canal like rings on a treeHaversian, or central canal: Central channel containing blood vessels and nervesVolkmanns canals: Channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal25

Interstitial Lamellae26Interstitial Lamellae that are not part of an osteonThey are incomplete lamellaeThey fill the gaps between forming osteons or are remnants of osteons that have been cut through by bone remodeling26

Circumferential Lamellae27Circumferential lamellae are deep to the periosteumExtend around the entire circumference of the shaft

2728

Concentric lamellae28

Microscopic Structure of Compact Bone29Spider-shaped osteocytes occupy small cavities known as lacunae at the junctions of the lamellae. Hair like canals called canaliculi connect the lacunae to each other and to the central canal.Canaliculi allow the osteocytes to exchange nutrients, wastes, and chemical signals to each other via gap junctions.

29Microscopic Structure of Spongy Bone30No osteons are presentLamellae are irregularly arranged into plates called trabeculae.Small needle-like pieces of boneHave a lot of open space between themFilled with bone marrow.Trabeculae are interconnected by canaliculiTrabeculae align precisely along lines of stress30

Spongy Bone31Osteocytes are nourished by diffusion from nearby Haversian canals The osteocytes are connected by canaliculi

31Bone Cells32Bone tissue is a type of connective tissue, so it consist of cells plus a significant amount of extracellular matrix.Osteoprogenitor Cells (osteogenic cells)Undergo mitosis and become osteoblasts Derived from mesenchyme32Osteoblasts 33Bone-building cells.Synthesize and secrete collagen fibers and other organic components of bone matrix. Releases calcium and phosphate ions for production of hydroxyapetiteInitiate the process of calcification.Found in both the periosteum and the endosteumCannot undergo mitosis33Osteoblasts34The blue arrows indicate the osteoblasts.The yellow arrows indicate the bone matrix theyve just secreted.

34Osteocytes 35Mature bone cells derived from Osteoblasts that have become trapped by the secretion of matrix Respond to stresses and remodel bone in response to those stressesMaintain daily cellular activitiesNo longer secrete matrix Cannot undergo mitosis Will transform back to an osteoblast when bone remodeling is needed. 35Osteocytes36Yellow arrows indicate osteocytes: notice how they are surrounded by the pinkish bone matrix.Blue arrow shows an osteoblast in the process of becoming an osteocyte.Green arrow: Osteoclast

36Bone CellsOsteoclasts 37Huge cells derived from the fusion of as many as 50 monocytes or macrophages (a type of white blood cell).Function in bone resorption (i.e. destruction of bone matrix that is part of normal bone growth, development, maintenance and repair) Breakdown of bone matrix with both acid phosphatase and HCLCollagen is broken down by the phosphatase (enzyme) and mineral are broken down by the HCL37Osteoclasts38

38Introduction to the Nervous System

The functional unit is the neuronThese are the cells that carry out the activity of nervous tissueNeuroglia (glial cells) aid neurons

Nervous SystemCentral Nervous System (CNS) brain and spinal cordPeripheral Nervous system (PNS)- cranial and spinal nerves, and ganglia

Neuron

3 main parts:AxonDendriteCell body (neurosoma)Neuroplasm (cytoplasm)Nissl bodies (RER)NucleusAxon hillock

Functions of neuronsSensory (afferent): conduct impulses to CNS.Convey info from the external or internal bodyMotor (efferent) conduct impulses away from CNSInterneurons (association) neurons occur between sensory and motor neurons

Neuron ShapesClassified according to shapeMultipolarBipolarUnipolar (pseudounipolar)

SynapsesNeurons transmit information electrochemically along the length of the axon to the synaptic knob.The junction is called the synapse and chemicals called neurotransmitters move across the synaptic cleft

PNS NeurogliaSchwann cells (neurolemmoctye) wrap around the axon, leaving small gaps between successive cells called the nodes of Ranvier.Consist of a lipoprotein called myelin and a series of schwann cells forms the myelin sheath.Allows nerve transmission to jump from node to node, increasing speed called saltatory conduction

Histology of a Nerve

CNS NeurogliaOligodendrocytes have the same function in the CNS as Schwann in PNSMyelinated nerve fibers appear white so are called white matter

CNS NeurogliaThe most common glial cells are the astrocytes.Form blood-brain barrierNourish neuronsRelease nerve growth factors among other things.

CNS NeurogliaMicroglia are small, phagocytic glial cells.They resemble macrophages as they engulf microbes or damaged tissue

CNS NeurogliaEpendymal cells line the ventricles of the brain and modify the cerebrospinal fluid

Specialized NeuronsPyramidal cells are found in the cerebral cortex of the brainPurkinje cells are common in the cerebellum.